Re: Paired shots from different focal lengths

[P3D John Bercovitz <bercov@xxxxxxxxxx>]

>> On the surface this is true BUT we also jiggled the images 
>> to the same image size and DEPTH OF FIELD IS EQUAL AT THE SAME 
>> F/STOP AT THE SAME MAGNIFICATION REGARDLESS OF FOCAL LENGTH.
 
> Almost: f/number is relative aperture but the DOF is the same at 
> the same _linear_ aperture (hole-in-the-iris size).  So if we 
> took a picture with a 100 mm lens at f/8 and then took a picture 
> from the same point with a 50 mm lens at f/4 but blew it up 2X, 
> the DOF would be exactly the same.  It's an easy experiment to 
> try and most folks have these two lenses for their SLRs so give 
> it a go.
 
Oops!  I wasn't paying attention.  You said "at the same
magnification" and of course you're absolutely right.  I missed 
the change in gears: I thought we were still talking about taking 
pictures from the same vantage point.  Mea culpa.

Now to get the same magnification, you have to back up to twice 
the distance from camera to subject when you go to twice the
lens focal length.  Now your perspective is all changed.
 
John B


------------------------------